This application will examine sleep and sleep disturbance in the elderly, seeking to develop an alternative method for improving sleep quality in the elderly. Forty elderly female volunteers with sleep maintenance insomnia will participate in a 10-day/night protocol involving a comparison of the effects of Passive Body Heating (PBH) and a commonly used hypnotic (zolpidem) on sleep, temperature, growth hormone secretion, subjective sleepiness, and performance. Baseline actigraphic and sleep diary data will be collected for ten days prior to the study to evaluate sleep at home and to confirm insomnia. Subjects will be randomly assigned to one of four treatment conditions: PBH/placebo, PBH/zolpidem, PBH control/placebo, PBH control zolpidem. The PBH intervention will involve having the subjects sit in a tub filled with 40 C (active) or 37 C (control) water for 30 minutes. Zolpidem will be administered at 5mg. Objective measures of sleep will be quantified using standard sleep scoring criteria. Changes in sleep efficiency and architecture will be measured and amplitude and density of slow wave sleep will be quantified using power spectral analysis. Subjective measures of sleep will be taken using a post-sleep questionnaire and a visual analog scale. Core body temperature and motor activity will be recorded continuously using ambulatory monitoring systems. Growth hormone will be sampled every 30 minutes during one baseline and one treatment night and assayed using standard procedures. Measures of memory, reaction time and vigilance will be made during the day. The PBH technique may achieve the same beneficial effects on sleep as zolpidem, with the risk of side-effects associated with hypnotic medication. The investigators intend to determine whether the PBH procedure will be a useful non-pharmacologic method for treating insomnia in the elderly.